"Another thing that makes canon a little confusing. Gene R. himself had a habit of de-canonizing things. He didn't like the way the animated series turned out, so he proclaimed that It was non-canon. He also didn't like a lot of the movies so he didn't much consider them canon either. And -- okay I'm really going to scare you with this one -- after he got TNG going, he... well... he sort of decided that some of the original series wasn't canon either. I had a discussion with him once, where I cited a couple of things that were very clearly canon on The Original Series, and he told me that he didn't think that way anymore, and that he now thought of TNG as canon whenever there was conflict between the two. He admitted that it was revisionist thinking, but so be it."
-- Paula Block, 2005
Oh, that is infinitely worse than George Lucas and his original trilogy tinkering. Insane the disrespect Roddenberry had for TOS (and TAS but that’s not as sacrosanct to many fans). He was not a well man physically or mentally by that point, some claim drug addled, so I don’t take Roddenberry’s fits of decanonisation at all seriously.